The US economy will naturally expand through sex and immigration, so at some point, despite how rubbish the market is, there will be a natural tendency to start seeing new house builds at some point.

If all you are finding is a few mismatched pieces of furniture with no clear value, and a lot of rubbish, maybe some personal items strewn about, with no "normal" indicators of current use, and especially if utils are off; or if you find the house keys sitting on the kitchen counter or hanging by the door, these are all pretty good indicators it has been abandoned.

I know the purchase price, but I have no idea what else I would need to spend to get this sell ready.I've looked at the county records and can find various liens for weeds, rubbish, and nuisance, but I believe (not confirmed) there are environmental issues that is keeping everyone away from it.How do I go about finding out if there are environmental issues to take care of and anything else that I would have to plan for in terms of rehab and outstanding issues? 

Additionally options like Craigslist or Facebook marketplace have been solid for me to get people for rubbish cleanups I've had in the past.

Rubbish.

If, however it truly gets out of hand to a point of creating a fire hazard or impeding the ability to make a reasonably hasty exit; or if they are completely blocking an exit or an electrical panel; or excessively stockpiling recyclables or flammable material; if food has been clearly left out for extended periods, with roaches crawling all over it or worse, and household rubbish is not being reasonably contained, I will give them ONE 30 day period to make dramatic improvement, a second violation would result in non-renewal or termination for cause.

TENANT(S) shall not allow any flushable wipes, tampons, condoms, sweepings, rubbish, sand, rags, ashes or other substances to be thrown or deposited therein.

Typically they will need to schedule a move out inspection with you, and know that they need to have all personal property removed, tenant damages repaired, thoroughly clean the entire unit, all fixtures, windows, screens; carpets need to be professionally cleaned (and allowed at least a full day to dry before the inspection), and how they are expected to handle their rubbish.

Often there is nothing needed...but, yes, occasionally a unit will need rubbish hauled out and repairs, but these are the exception, as far as Tenants I have placed.

They must leave unit clean and free of all personal property and rubbish.